The present assignee's U.S. Pat. Nos. 5,654,696 and 5,475,375 disclose electronic security systems in which a palmtop computer is used as a key. In the detailed systems, no modification is made to the computer; the computer and lock communicate via standard infrared ports. The lock opens if the correct signals are exchanged.
While advantageous in many respects, the systems detailed in those patents have certain limitations. For one, the locks must have infrared interface capabilities. While such capabilities can be incorporated into new locks, the large installed base of existing locks without infrared capability cannot be used in such systems. (A sampling of such locks is shown in commonly-owned U.S. Pat. Nos. 4,727,368, 4,766,746, 5,280,518, 5,550,529, and 5,758,522.)